Disentangling / unmasking

Alain Moren, Dublin, 2006

What is behind: The epidemic curve The rate

Behind the epidemic curve ?

Hepatitis A by date of onsetOgemaw county, Michigan, April - May 1968

2 8 14 20 26 2 8 14 20 26 1 7

Days

0

5

10

15

Number of cases

one case 30 days

15 days

50 days

Exposure

Cases of Legionnaires disease and control measures implemented at plant N, Lens, France, 2004

N cases

9

8

7

6

5

4

3

2

1

5-7

8-1

0

11

-13

14

-16

17

-19

20

-22

23

-25

26

-28

29

-1

2-4

5-7

8-1

0

11

-13

14

-16

17

-19

20

-22

23

-25

26

-28

29

-31

1-3

4-6

7-9

10

-12

13

-15

16

-18

19

-21

22

-24

November December January

CT stopped Plant closedCT restarted

Cleaning and disinfection Lagoon ventilators stopped

01

23

45

67

Normal plant operations Re-operation of CT

Chemical water treament

Cleaning operations

Lagoon ventilators shut down

22/10 01/11 15/11 01/12 15/12 01/01 15/01 01/02

nb

of

ca

se

s

01

23

45

67

2003 2004

Gastroenteritis by day of onset

1 2 3 4 5 6 7 8 9 10 11 12 13

Days

0

10

20

30

40

50Cases Common

source ?

Person to person ?

Number of cases

One case

Cases of gastroenteritis among residents of a nursing home, by date of onset, Pennsylvania, October 1986

18 19 20 21 22 23 24 25 26 271716151314Days

0

5

10

Protein Total Cases AR% RRsuppl.

YES 29 22 76 3,3

NO 74 17 23

Total 103 39 38

Cases of gastroenteritis among residents of a nursing homeaccording to protein supplement consumption, Pa, 1986

Number of cases

One case

Early cases of gastroenteritis among residents of a nursing home, by date of onset, Pennsylvania, October 1986

18 19 20 21 22 23 24 25 26 2717161513 140

5

10

Days

Protein Total Early AR% RR CI 95%suppl. cases

YES 29 14 48 6.9 3,2-15,8

NO 74 5 7

Total 103 19 19

Early cases of gastroenteritisaccording to protein suppl. consumption

Early cases = onset < 21 October

Number of cases

One case

Late cases of gastroenteritis among residents of a nursing home, by date of onset, Pennsylvania, October 1986

18 19 20 21 22 23 24 25 26 271716151314Days

Protein Total Late cases AR RR CI 95%suppl. %

YES 10 3 30 2,5 0,7 - 8,9NO 65 8 12

Total 75 11 15

Late cases of gastroenteritis according to protein suppl. consumption, Pa, 1986

Late cases = onset > 20 October

Protein Total Early cases AR RR CI 95%suppl. lab. + %

YES 29 10 35 11,7 4,2- 38,7

NO 74 2 3

Total 103 12 12

Early cases of gastroenteritis lab. confirmed according to protein suppl. consumption, Pa, 1986

Cases of gastroenteritis by date of onset, Latuque, Quebec, 1989

7-11 8-11 9-11 10-11 11-11 12-11 13-11 14-11 15-11 16-11 17-11 18-11 19-11 20-11

0

10

20

30

40

50

60

70

Date of onset

Cases of gastroenteritis by date of onset, Latuque, Quebec, 1989

7-11 8-11 9-11 10-11 11-11 12-11 13-11 14-11 15-11 16-11 17-11 18-11 19-11 20-110

10

20

30

40

50

60

70

Date of onset

Cases of NLV gastroenteritis in a village, Sweden, 2002

20 No. of cases19181716151413121110987654321

16 17 18 19 20 21 22 23 24 25 26 27 28 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

Date of onset

Late cases

Early cases

February March

Cases

10

9 One case8

7

6

5

4

3

2

10

30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2

January

week numberNovember DecemberAugust September October

Risk factorsRestaurantHotelShop

Cases

10

9 Restaurant8 Shop7 Hotel6 Others5 x4

3 y2

10 z

30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 1 2

January

week numberNovember DecemberAugust September October

Cases of hepatitis A in Ibizaby group of patients, 2001

Events

Person - time denominator

Behind the rate ?

Sum of individual contributionDenominator

Vaccine efficacyVaccine efficacy

Attack rate among vaccinated Attack rate among non vaccinated

Vaccinated

Not vaccinated

% with disease

% with disease

Epidemic duration

VE based on attack rates (cumulative incidence)

VE =VE =ARNV - ARVARNV - ARV

ARNVARNV

Assumptions

Vaccine status as noted at begining of epidemic Vaccine status does not change during epidemic Epidemic duration is short Disease status as noted at the end of the epidemic

If interested in VE by age group: ==> one individual stays in same age group

during entire epidemic

Incidence density rate among non vaccinated Incidence density rate among vaccinated

VE =VE =IDRNV - IDRVIDRNV - IDRV

IDRNVIDRNV

Rates expressed in person-time

VNVNV

6 0

V

V

V

V

NV

2.5 3.5

6 0

3 0

0 3

2.5 1

D

M

NV

MNV

Measles epidemic, duration = 6 months

V0 6

NV

<6 6-8 >= 9 m65 14 23 32 3 11 3 2 3 3 2 4 1 5

012345678

Age (month) at beginning of epidemic

Time spent in each Age group

Epidemic duration = 6 months

Information needed

Date of start and end of epidemic Date of birth Date of death Date of onset of measles Incubation period (median) Delay for protection from vaccine